Industrial fabrics used in filtration and conveying applications, such as papermaking and the like, are typically formed by interweaving a plurality of polymeric yarns (such as monofilaments, multifilaments, cabled yarns and the like) according to a chosen pattern using an industrial loom. The fabrics are usually woven flat and then subsequently joined along their longitudinal edges by a seam. The fabrics may also be woven without ends, in a tubular form, to a specified width and length, and subsequently installed on a particular machine. Such fabrics can also be produced from one or more modules of nonwoven yarn arrays in which the component yarns are laid parallel to one another and held in place by adhesives and batt material needled through the array.
These fabrics are highly specialized constructions that are designed to be uniquely suitable for their intended end use application. Due to the relatively high cost of equipment required to assemble these fabrics, as well as the specialized labour force needed to guide them through various stages of production, manufacturers have searched for lower cost alternatives for their manufacture.
While nonwoven fabrics are more easily produced, there are the many structural requirements imposed by the manufacturing environments. For example, papermaking fabrics designed for use in the forming, press or dryer sections of the papermaking machine, must provide a uniformly smooth, but porous, surface layer to the paper product. The fabrics must be capable of withstanding mechanical forces when running at speeds of 1,000 m/min or more. They must provide an opposing layer resistant to thermal and chemical degradation, as well as abrasion, so as to provide the purchaser with satisfactory performance and service life.
Until recently, it has been very difficult for manufacturers of these industrial fabrics to provide a wholly nonwoven product which satisfies all of the above requirements. Furthermore, the formation of a nonwoven fabric from two or more layers with different properties presents additional problems, as discussed below.
U.S. Pat. No. 5,983,467 discloses the joining of two surfaces by a set of islands provided on one surface engaged within apertures provided on a second surface. The islands are arranged so that there are apertures between sets of adjacent islands. The joined surfaces may be disconnected and reconnected.
U.S. Pat. No. 6,124,015 discloses an industrial fabric having at least one segment including at least one woven or nonwoven ply joined either to itself, or to another ply (or segment) by use of structures or jointing yarns (e.g. hook and loop, or rib and slot) that interlock with each other to form a lap join.
U.S. Pat. No. 6,902,787 discloses a permeable industrial fabric that is assembled from tiles arranged in at least two plies. The two plies are held together by jointing structures that are integral with the tiles. Within each tile, the jointing structures are incorporated at primary selected locations according to a symmetrical pattern. Apertures in the tiles, which provide fabric permeability, are incorporated at secondary and tertiary selected locations according to two more patterns, at least one of which is asymmetrical.
Industrial fabrics formed by mechanically interconnecting one fabric layer or component with a second by means of a fastening arrangement have been disclosed; for example, U.S. Pat. No. 7,220,340 which describes a nonwoven papermaker's dryer or press fabric comprising a layer of MD (machine direction) yarns overlaid with a layer of CD (cross-machine direction) yarns. The yarns are positively connected to one another at their crossing points by one or more of the following: an adhesive, snap-fit (i.e. a peg and hole arrangement such as rivet-type fastener) or by localized melting at the crossing points.
PCT patent application publication WO 2011/069259 discloses industrial fabrics formed from two or more layers of a slit and profiled plastic film having specific characteristics; similar film fabrics have been further described by CA 2,779,969, CA 2,779,131 and CA 2,791,864 (presently unpublished). Other nonwoven fabrics including one or more film layers are known and have been described in WO 2012/028601, WO 2012/095251, WO 2012/100161, WO 2005/042836, WO 2008/145420, WO 2003/068495 and GB 1037003, for example.
US 2003/0190451 discloses an industrial fabric comprising at least two separate layers. The layers are joined by pairs of interlocking structures, with each interlocking structure integral with each layer. The resulting joining of the layers provides a void volume between the layers. The layers may be made from differing thermoplastics so that each layer has different physical properties. The layers may be porous or non-porous.
US 2012/0021171, US 2012/0027997, US 2011/0272112, US 2010/0239814, US 2010/0236740, US 2010/0236034 and US 2010/0230064 disclose various nonwoven film-type industrial fabrics which may include a topographical pattern on a product contact side. However, none of these documents discloses a mechanical interlocking of two or more layers of film or sheet material in which integral protrusions of a first layer are lockably engaged with at least one detent in a second layer.
In the present disclosure, it is shown that a mechanical fastening process may provide the desired flexibility of materials used in each of the layers of an industrial fabric, while simplifying the process by which these layers are interconnected to the one another. It has been found that, by means of the present invention, it is now possible to interconnect two similar or dissimilar profiled and apertured film or sheet materials by means of a mechanical interlocking process such as, hot staking or clinching. By interconnecting the two or more film layers by means of such mechanical fastening process, it is now possible to provide the optimal desired properties to each layer, independently of the properties provided to other layers.